AM_MEDIA_TYPE

This structure describes a media sample type.

typedef struct  _MediaType{
  GUID majortype;
  GUID subtype;
  BOOL bFixedSizeSamples;
  BOOL bTemporalCompression;
  ULONG lSampleSize;
  GUID formattype;
  IUnknown* pUnk;
  ULONG cbFormat;
  /* [size_is] */ BYTE __RPC_FAR* pbFormat;
} AM_MEDIA_TYPE;

Members

• majortype
  Major type of the media sample.
• subtype
  Subtype of the media sample.
• bFixedSizeSamples
  If TRUE, samples are of a fixed size.
• bTemporalCompression
  If TRUE, samples are compressed.
• lSampleSize
  Size of the sample in bytes.
• formattype
  Registered (GUID) format type.
• pUnk
  Pointer to the IUnknown interface.
• cbFormat
  Size of the format section of the media type.
• pbFormat
  Pointer to the format section of the media type. The layout of this is determined by the format type GUID. Format types include the following.

  Format type	Structure pointed to
  FORMAT_MPEGVideo	MPEG1VIDEOINFO
  FORMAT_VideoInfo	VIDEOINFOHEADER
  FORMAT_WaveFormatEx	WAVEFORMATEX
  FORMAT_MPEG2Video	MPEG2VIDEOINFO
  FORMAT_VideoInfo2	VIDEOINFOHEADER2

Remarks

Media Types

In any function that receives an AM_MEDIA_TYPE parameter, always validate the values of cbFormat and formattype before dereferencing the pbFormat member.

The following code is incorrect:

if (pmt->formattype == FORMAT_VideoInfo)
{
    VIDEOINFOHEADER *pVIH = (VIDEOINFOHEADER*)pmt->pbFormat;
    // **** Wrong! ****
}

The following code is correct:

if ((pmt->formattype == FORMAT_VideoInfo) && 
    (pmt->cbFormat > sizeof(VIDEOINFOHEADER) &&
    (pbFormat != NULL))
{
    VIDEOINFOHEADER *pVIH = (VIDEOINFOHEADER*)pmt->pbFormat;
    // Now you can use pVIH.
}

Requirements

DirectShow applications and DirectShow filters have different include file and link library requirements. See Setting Up the Build Environment for more information.

OS Versions: Windows CE 2.12 and later. Version 2.12 requires DXPAK 1.0 or later.
Header: Dshow.h.

Last updated on Wednesday, April 13, 2005

© 2005 Microsoft Corporation. All rights reserved.